Film cameras of the type typically used in professional cinematographic production provide the camera operator with an optical image corresponding to the image exposed on film. With the advent of compact video components, professional motion picture cameras have been modified to employ a video pickup (often referred to as a “video tap”) built into the film camera in order to facilitate certain cinematic decisions about the captured image and to allow other people to view the image seen by the camera operator through the viewfinder eyepiece.
The video tap shows the whole of the image area recorded at the film gate together with a superimposed bright outline, generated electronically from the signal processing unit, to indicate the limit of the projected frame area so that the picture can be accurately composed. When using an anamorphic camera lens, the monitor image may be electronically unsqueezed so that the picture is shown in its correct proportions (see U.S. Pat. No. 5,883,696, in which the video system de-anamorphises the image displayed on the video monitor when anamorphic lenses are used in the film camera.). The picture is often a black and white television image rather than the actual colors of direct viewing but this is not regarded as a disadvantage. The main function of the video viewfinder normally is to check the composition of the scene, to follow the action to adjust focus as required and to generally make artistic decisions based on scene content. The definition and color reproduction characteristics of color television systems differ considerably from those of film and it is considered that a color monitor presentation would be of doubtful value even if it were conveniently and economically available.
Consequently, video taps are neither capable nor intended to predict the actual film look of a captured image sequence after it is post-processed and projected. This is understandable because there are numerous film stocks available to choose from for a video or motion picture production. Each of these film stocks has its own unique set of characteristics and capabilities, which ultimately influences the appearance of the captured scene. The viewed image from a video tap, however, does not necessarily reflect the exposures resultant on a film of interest, nor the appearance the scene would have after being recorded on the chosen film, processed and subsequently viewed.
Presently, a variety of methods are utilized to predict the look of a captured image sequence. One of those methods relies on a cinematographer's experience. An experienced cinematographer can relate how a setting under a specific lighting condition will look when it is finally processed for viewing. The problem with this method is that it is neither accurate nor consistent and it cannot be easily shared with others, as the predicted look of the image-sequence only exists in the cinematographer's mind.
Another method for predicting the look of a captured image sequence involves filming a representative scene and exposing the film under a variety of conditions which the cinematographer thinks will result in a captured scene having the desired appearance. The film is then processed overnight for viewing the next day (daily). Often the film is transferred to video via a telecine machine and viewed the next day on a video monitor (video daily). After viewing the processed, captured sequence the next day, a cinematographer will decide if the image sequence of interest needs to be shot again, or if the results were satisfactory. The problem with this method is that it does not provide real-time feedback and it is relatively costly.
The difficulties and high costs associated with dailies highlights the need for a device that could provide less expensive, reasonably accurate and more timely feedback concerning the cinematographer's predictions and adjustments for the lighting conditions of any scene. Another method for predicting the look of a captured image sequence is described in U.S. Pat. No. 6,122,006, which involves the initial capture of a still image for a particular set under a certain lighting condition using an instant photographic or electronic camera. The captured image is then scanned or downloaded into a computer, where it is digitally processed to simulate the desired look of a recorded image-sequence using a particular film. Once the desired look is obtained, the cinematographer uses a motion picture camera to capture the scene using the same film as selected in the simulated software. Although this method can provide a cinematographer feedback in a less expensive and more timely manner, this feedback is not instant and is limited to a still image that is not contemporaneous with motion capture, thus affecting accuracy. Moreover, no motion-based decisions such as the introduction of blur due to the image averaging effect of viewing motion sequences can be inferred from it.
In a typical digital motion camera, as well as the film cameras described above, a captured image sequence takes two processing paths. The first path involves the recording of the captured image sequence to a particular media (e.g., film, tape, or disk). The other path involves the displaying of the captured image sequence by an electronic monitor (e.g., the video tap). As explained above, a video display would potentially allow a cinematographer to make artistic decisions based (only) on scene content. It does not, however, allow the cinematographer to view how the final recorded scene will look after being processed and ultimately displayed in accordance with a particular post-production process.
There are a variety of methods known in the prior art for electronically capturing and processing an image sequence in real time separate from the main capture path. For instance, in U.S. Pat. No. 5,926,218, a low-resolution image sensor is used separate from a high-resolution image sensor in an electronic camera for viewing and camera control functions. Besides using the low-resolution sensor to generate a low-resolution output signal for a display device, the low resolution output is applied to a zoom interpolator, which processes the low resolution output signal so that the size of a display image obtained from the low resolution signal corresponds to the zoom setting of the zoom lens in front of the high resolution sensor. In this way, the projected display simulates the look of the zoomed high resolution image.
U.S. Pat. No. 4,714,962 describes a dual electronic camera that concurrently exposes a conventional photographic film and an electro-optical sensor, to provide both corresponding electronically recorded images and photographic latent images of objects. The electronic images are then viewed using an optical pre-viewer for “proofing” purposes, that is, to select those to be developed and printed. The capability to instantly preview the images before development of the film enables the user to select the film negative frames to be printed, as well as controlling the conditions of developing and printing of the film to correct for exposure of each frame. For example, the instant optical previewing allows the user to determine whether the image has been overexposed or underexposed. The viewing of the electronic image thus permits instructions to be imprinted on the film for these and other corrections, such as cropping, enlarging, reducing, and physically displacing portions of the image. In this patent, while the viewed images provide a photographer with the chance to proof an image frame based on scene content considerations, it is limited to still photography and does not allow a judgement based on how the captured images will look after being processed (and printed).
U.S. Pat. No. 5,852,502 describes a digital motion camera that has an optical assembly that directs visual images to a high-resolution monochrome sensor and a lower resolution color sensor. At any instance of time the two captured images using both sensors are composited to produce a high-resolution color composite image output. One copy of the image may be recorded using a film or digital recorder, and another copy may be projected on a display device. Even though a digital image processing algorithm is being applied to the captured image-sequence before viewing it, the purpose of this processing is to composite the color and luminance information of an image to produce a high-resolution colored image sequence. Although this patent allows for the image processing to provide a non-linear emphasis of particular ranges of colors, such as darker colors, mid range colors or a specific color, it is not the objective of this processing to match any post-processing that might later take place on the recorded captured sequence of images.
Prior art also exists for generating a broadcast film appearance with video or digitally captured images, where the processing occurs inside of the camera. In U.S. Pat. No. 5,475,425, a video camera provides for real time simulation of the visual appearance of motion picture film that has been transferred or converted to a video signal, by adding a selective adjustable amount of two-dimensional electronic artifacts to simulate film grain and by modifying the scan rate of the electronic sensors to imitate film shuttering. This video camera, however, is not providing any display of the processed video, and particularly is not operating on unprocessed RGB signals to provide a real time display image. In an article by L. J. Thorpe et al, “The HDTV Camcorder and the March to Marketplace Realty”, SMPTE Journal, March 1998, pp. 164–177, setup cards have been described for beta-camcorders and also digital camcorders. These miniature plug-in setup cards facilitate prealignment of the camera to achieve an HD image having attributes similar to those that might otherwise be created from a film origination followed by telecine transfer to HD video. The setup cards can be pre-programmed to store desired digital data settings for aesthetic choices to be made concerning, among other characteristics, color reproduction, tonal reproduction and skin-tone detail. In both of these disclosures, however, there is no effort to match the in-camera processing to a subsequent suite of algorithms that would be applied to the digital image signal in a post-production process.
What is needed is a method and/or a device that could provide inexpensive, instant and accurate feedback concerning a cinematographer's predictions and adjustments for the lighting conditions of any scene, based on how particular post-production processing will affect the look of the captured image sequence.